"No one ignored the hazards," Leon Panetta wrote in a letter published in the Washington Post, responding to those who questioned CIA tactics in eastern Afghanistan on a weekend during which some of the dead officers were laid to rest.

The revelations come hours after a tape was released in which the suicide bomber and double agent, Dr. Human Khalil al-Balawi, said he was motivated by revenge against the United States.

"This [suicide] attack will be the first of the revenge operations against the Americans and their drone teams outside the Pakistani borders," Al-Balawi said.

He added that he was avenging the death of Baitullah Mesud, the former head of the Pakistani Taliban.

The Jordanian doctor made his statement in English as he sat next to the leader of the Pakistani Taliban.

The CIA has been stung by accounts that suggested Al-Balawi was whisked past security checkpoints in Khost and was welcomed by a large group of U.S. agents. Panetta lashed out against such criticism.

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"Public commentary [is] suggesting that those who gave their lives somehow brought it upon themselves because of 'poor tradecraft,'" he wrote. "That's like saying Marines who die in a firefight brought it upon themselves because they have poor war-fighting skills."

Panetta and U.S. sources added new details about the bombing at the CIA base. The double agent was driven past security checkpoints that the Taliban are thought to monitor and arrived inside the base. As he exited the car, his hand was in his pocket.

"The individual was about to be searched by our security officers -- a distance away from other intelligence personnel -- when he set off his explosives," said Panetta.

Some of those intelligence officers were 50 feet away, but still were hit by shrapnel.

But the criticism continues.

"You can't sacrifice basic tradecraft under pressure from headquarters," former CIA officer Frank McGovern told ABC News. "Here was a fellow who pretended to be tied in with the top al Qaeda leadership, so all kinds of shortcuts were made."

While unable to give specifics, Panetta said his agency has been successful against terrorists and will continue the fight.